Joost Isenbaert, d. 25 August 1673, was an elder of the Flemish congregation of Middelburg, Dutch province of Zeeland, after 1637. He was a man of conservative principles and in 1659 fell into disharmony with his colleagues Adriaan van Eeghem and Pieter Baart, whom he accused of Socinianism. In 1665 he brought a charge before the city government against Adriaan van Eeghem and Thomas van Eeghem (who in 1663 had succeeded Pieter Baart after the latter had moved to Vlissingen). Both preachers were suspended and only Isenbaert was allowed to preach. But most members took the side of the van Eeghems. A schism in the congregation threatened but was prevented by the conciliatory attitude of Adriaan van Eeghem in December 1665.